Comparative phylogeography of two colonial ascidians reveals contrasting invasion histories in North America
Surveys of genetic structure of introduced populations of nonindigenous species may reveal the source(s) of introduction, the number of introduction events, and total inoculum size. Here we use the mitochondrial cytochrome c oxidase subunit 1 (COI) gene to explore genetic structure and contrast invasion histories of two ecologically similar and highly invasive colonial ascidians, the golden star tunicate Botryllus schlosseri and the violet tunicate Botrylloides violaceus, in their global and introduced North American ranges. Haplotype and nucleotide diversities for B. schlosseri were significantly higher than for B. violaceus both globally (h = 0.872; π = 0.054 and h = 0.461; π = 0.007, respectively) and in their overlapping North American ranges (h = 0.874; π = 0.012 and h = 0.384; π = 0.006, respectively). Comparative population genetics and phylogenetic analyses revealed clear differences in patterns of invasion for these two species. B. schlosseri populations on the west and east coasts of North America were seeded from the Pacific and Mediterranean regions, respectively, whereas all North American B. violaceus populations were founded by one or more introduction events from Japan. Differences in genetic structure of invasive populations for these species in North America are consistent with their contrasting probable introduction vectors. B. schlosseri invasions most likely resulted from vessel hull fouling, whereas B. violaceus was likely introduced as a ‘fellow traveler’ in the shellfish aquaculture trade.
KeywordsNonindigenous species Mitochondrial DNA Introduction Tunicates Botryllus schlosseri Botrylloides violaceus
We acknowledge our Canadian Aquatic Invasive Species Network (CAISN) colleagues G. Arsenault, J. Davidson, J. Hill, and A. Ramsay as well as our global colleagues T. Bolton, P. Chevaldonné, R. Graille, E. Grey, A. Izquierdo-Munoz, B. de Ligondes, S. Lopez-Legentil, J.-M. Nicolas, M. Ruis-Viladomiu, Y. Saito, X. Turon, and B. Vercaemer, who have so generously provided tunicate samples. D. Heath, S. Xu and A. Zhan provided valuable comments on an early draft of the manuscript. We also thank A. Adebayo, K. Laroche and R. Hepburn for assisting with lab work. This work was supported by CAISN, Fisheries and Oceans Canada and by NSERC Discovery grants to MEC and HJM.
- Avise JC, Arnold J, Ball RM, Bermingham E, Lamb T, Neigel JE, Reeb CA, Saunders NC (1987) Intraspecific phylogeography: the mitochondrial DNA bridge between population genetics and systematics. Annu Rev Ecol Syst 18:489–522Google Scholar
- BCMAL (2007) Shellfish aquaculture: current statistics. British Columbia Ministry of Aquaculture and Lands, BC, 108 ppGoogle Scholar
- Berril NJ (1950) The Tunicata, with an account of British species. Ray Society, London, iii+354ppGoogle Scholar
- Carlton JT (2005) Setting ascidian invasions on the global stage. International Invasive Sea Squirt Conference. Woods Hole Oceanographic Institution, Woods HoleGoogle Scholar
- Carver CE, Mallet AL, Vercaemer B (2006) Biological synopsis of the colonial tunicates, Botryllus schlosseri and Botrylloides violaceus. Canadian Manuscript Report of Fisheries and Aquatic Sciences 2747: v+42pGoogle Scholar
- Cohen AN, Carlton JT (1995) Biological study. Nonindigenous aquatic species in a United States estuary: a case study of the biological invasions of the San Francisco Bay and Delta. A report for the US Fish and Wildlife Service and National Sea Grant College Program. National Technical Information Service, Springfield, p 246Google Scholar
- Fay RC, Vallee JA (1979) A survey of the littoral and sublittoral ascidians of southern California, including the Channel Islands. Bull South Calif Acad Sci 70:114–124Google Scholar
- Meenakshi VK, Senthamarai S (2006) First report on two species of ascidians to represent the genus Botryllus Gaertner, 1774 from Indian waters. J Mar Biol Assoc India 48:100–102Google Scholar
- Nei M (1987) Molecular evolutionary genetics. Columbia University Press, New YorkGoogle Scholar
- Pallas PS (1766) Elenchus zoophytorum sistens generum adumbrationes generaliores et specierum cognitarum succinctas descriptiones cum selectis auctorum synomymis. Varrentrapp, F, Frankfurt, p 539Google Scholar
- Swofford DL (2001) PAUP*: phylogenetic analysis using parsimony (*and others methods). Sinauer, SunderlandGoogle Scholar